Preferred/popular grip sizes have decreased somewhat for the modern game. I have rather long fingers. Back in the day, I was using a 5 grip but in the past 20+ years, I am most comfortable with a 4 grip. Don't even see 5 grips in stock very often these days. More common to see 3 and 4 grip sizes.
I believe that the smaller grip size may be more conducive to employing wrist action and, possibly, more forearm rotation on groundstrokes. The greater topspin (and other spins) we see in the modern game can be generated with more forearm rotation and more wrist action. In days gone by, the wrist remained fairly firm for much of a stroke -- especially before and during the contact phase. I am not suggesting that your strokes should become very wristy but there will be some wrist release before and after contact.
If you are prone to wrist, forearm or elbow injury, you might be better off with a larger grip. However, a grip that is much too large could result in GE or other issues if you are gripping too tightly (too much of the time). With the proper grip size, you should be able to maintain a fairly relaxed grip that will firm up naturally as the racket head is accelerated into contact. On your follow-thru your grip should be, once again, relaxed. With a grip that is much too small or too large, this might be more difficult to do.